Magnetic circuit for an electric wrist watch



Oct. 4, 1960 P. E. BIEMILLER ET AL 2,954,664

MAGNETIC CIRCUIT FOR AN ELECTRIC WRIST WATCH 3 Sheets-$heet 1 Filed April 17, 1956 Fig. 2

INVENTOR Philip E. Bicmiller James H. Rule ATTORNEY Oct. 4, 1960 P. E. BIEMILLER ETAL 2,954,664

MAGNETIC CIRCUIT FOR AN ELECTRIC waxsr WATCH Filed April 1?, 1956 s Sheets-Sheet 2 INVENTOR Philip E. Biemillor James H. Reese ATTORNEY Oct. 4, 1960 P. E. BIEMILLER ETAL MAGNETIC CIRCUIT FOR AN ELECTRIC WRIST WATCH Filed April 1'7, 1956 III... I r k Fig.6

3 Sheets-Sheet 3 INVENTOR Philip E. Biomillcr Jana H. Run

BY W

ATTORNEY United States Patent MAGNETIC CIRCUIT FOR AN ELECTRIC WRIST WATCH Philip E. Biemiller, Landisville, and James H. Reese, Manheim, Pa., assignors to Hamilton Watch Company, Lancaster, Pa., a corporation of Pennsylvania Filed Apr. 17, 1956, Ser. No. 578,844 19 Claims. (01. 58-28 This invention relates to an electric wrist watch and more particularly relates to the magnetic circuit for the electric watch, wherein the balance wheel serves as the frequency controlling element and is periodically energized during passage through the magnetic field.

The limited space within the case of a wrist watch imposes stringent limitations upon both the primary electric source and the means for converting the electrical energy into mechanical energy. Further, it is obvious that the amount of electrochemical energy which can be built into a watch size battery is limited. This requires that the available electrical energy must be converted into mechanical energy as efiiciently as possible so that an extended battery life can be obtained. The component parts of the electric and the mechanical movement, must be kept to a minimum size. While many attempts have been made to solve this problem satisfactorily, we are not aware that any electric wrist watch has ever been suc cessfully marketed.

The electric motors for converting electrical energy to mechanical energy in an electric wrist watch heretofore proposed have been both of the moving coil and stationary coil type and have generally used stationary or movable permanent magnets of various shapes. Watches using permanent magnets have been found impractical in part because the magnets have necessarily, due to the need for some minimum flux density, been formed more or less elongated. In certain constructions shunts or keepers have been used with such magnets and in still other constructions the magnets have been bent into U-shapes. While these arrangements might be feasible in clocks, the lack of space in wrist watch installations results in low efficiency motors and also in extensive stray magnetic fields.

Stray magnetic fields are detrimental in that they magnetize steel parts within the watch. They make it necessary to provide nonmagnetic balance staffs to prevent a magnetic influence which will alter the isochronical behavior of the frequency controlling element. Stray magnetic fields affect hairsprings. Hairsprings must be temperature compensating for quality timepieces and this is commonly accomplished by using alloys having certain magnetic characteristics.

We have now discovered that these problems of stray fields, adequate flux density and size may be effectively minimized through the use of magnets and magnetic circuits of certain specific shapes and magnetic materials. We have thus found that advantages may be obtained by discarding the conventional elongated bent or unbent magnets heretofore utilized and replacing these with cylindrical magnets having a length to diameter ratio substantially on greater than one which are associated with particular types of shunt circuits. Certain magnets having a length to diameter ratio of not greater than one fit well within the space available in wrist watches and when coupled with particular types of shunt constructions produce adequate flux density and efiectively minimize flux leakage.

2,954,664 Patented Oct. 4, 1960 ice It is well known that the amount of flux leakage between steel connecting portions of a magnetic circuit is dependent upon the distance separating these portions. In a wrist watch having a permanent magnetic circuit, space limitations prevent extreme separation of these steel portions. Within these space limitations we have. endeavored to separate the upper and lower shunts as far as possible.

Flux leakage is also a function of the length of the steel connecting portions of a magnetic circuit and it is advantageous to keep said steel portions to reasonable limits in length. The embodiment shown is a compromise between separations of steel portions and lengths of steel portions in a magnetic circuit and is expressed in the watch by the configuration of the lower and upper shunt pieces.

With the major portion of the lower shunt out of vertical alignment with the magnets and the major portion of the upper shunt, while maintaining length limitations, flux leakage between the two shunts is minimized.

The passage of the excited coil beneath the shunt will induce eddy currents in the shunt. To break up the path and to reduce these currents, the upper shunt was made of odd configuration. It was found by experiment that the shape shown produced the most efficient motor. Stray fields are practically eliminated and the eddy currents reduced.

It is, accordingly, a p'rimary object of the present invention to provide an electric wrist watch operating from a self-contained battery and having a high efiiciencyof conversion of electrical to mechanical energy.

It is another object of the invention to provide an electric wrist watch including a small but powerful source of permanent magnetism arranged in a magnetic circuit which minimizes stray fields.

It is another object of the invention to provide an electric watch having a novel magnetic shunt circuit which minimizes flux leakage and provides a uniform field in the air gap.

It is a still further object of the present invention to provide a pair of magnets in close proximity, the one to the other, with opposite poles uppermost and a shunt bridging both magnets.

It is a further object of the present invention to provide, in an electric wrist watch, a pair of magnetic fields in which the magnetic flux is in different directions.

It is a still further object of the present invention to provide a pair of magnets arranged adjacently having unlike poles uppermost to create a pair of magnetic fields having the flux in opposite directions and to bridge both of said fields with a single shunt.

It is a still further object to provide a pair of magnets creating a pair of magnetic fields having the flux in opposite directions and a shunt for restricting said flux, said shunt leaving the greater area of the ends of the magnets uncovered.

It is a still further object of the present invention to provide a single shunt for a pair of magnets arranged with unlike poles uppermost and leaving the greater part of the magnets uncovered, said shunt being of irregular design to reduce eddy currents.

It is a still further object of the present invention to provide a magnetic circuit having upper and lower shunts with cylindrical magnets between said shunts, said magnets having a length to diameter ratio of not greater than one and to have said lower shunt, magnets and upper shunt not in vertical alignment.

These and further objects and advantages of the invention will become apparent upon reference to the following specification and claims and appended drawings wherein:

Figure 1 is a plan view of the train side of an electric watch constructed according to the invention, with the balance cock removed.

Figure 2 is a vertical elevation of the watch of Figure 1.

Figure 3 is a perspective view of the magnet mounting assembly of the watch of Figures 1 and 2.

Figure 4 is a partial view of the train side of the watch of Figures 1 and 2 showing the upper shunt and magnets with the balance wheel removed.

Figure 5 is an elevation of the mechanism shown in Figure 4.

Figure 6 is a partial plan view of the dial side of the watch of Figures 1 and 2 showing the lower shunt in detail.

Figures 7 and 8 show a different type of shunt structure.

In creating a permanent magnetic field for use in electrically operated timepieces it has been customary to utilize magnets Whose length is relatively large compared to the diameter or width. Generally, these magnets have been bent into various configurations so as to fit within the watch case and still produce the desired flux density in the air gap. While the patent literature is for the most part silent as to the specific magnetic materials utilized, the magnet shapes used would seem to indicate that it was thought desirable to use magnetic materials having a high residual induction. According to our invention, we have found that, with wrist watches, markedly better operation may be achieved through the use of magnetic materials having balanced magnetic characteristics which may include a somewhat lower residual induction but which is offset by a larger coercive force and a suitable energy product for magnets having a length to diameter ratio of not greater than one, as particularly set forth in our co-pending application S.N. 578,843, filed April 17, 1956. While magnetic shunts or keepers have been commonly used heretofore, they have generally been used in conjunction with the aforementioned elongated magnets in assemblages where the magnet overlies the shunt or vice versa.

We have now found that stray fields may be controlled and practically eliminated and air gap flux density maintained at a uniform high value if the shunt elements do not overlie one another, and if the portions of the shunt adjacent the magnet poles do not substantially overlie the faces of the magnet from which the flux emanates.

Referring to Figures 1 through 3, there is seen an electric watch 42 constructed according to our invention. The watch 42, as seen from the train side in Figure 1, comprises a pillar plate 44 which supports a battery 46 held in place by means of a clip 48 and spring 50. The balance staff 52 carries a balance wheel 54 having a sector shaped coil 56 secured to the rim of said wheel by means of clamps 58 and 60. A roller table 62 is carried on the balance staff 52 above the balance Wheel 54 and carries a pin 64 and contact 66 for making periodic electrical contact with the contact spring arm assembly 68 which is connected to one terminal of the battery 46. Further details of the specific contact system may be found in 'assignees co-pending application S.N. 551,791, filed December 8, 1955.

Referring to Figure 3, the pillar plate 44 is provided with a sector shaped slot 70 under the balance wheel 54 and adjacent to the inner portion of this slot the pillar plate is apertured to receive a pair of cylindrical magnets 72 and 74 which are press fitted therein and which have a length to diameter ratio of substantially no more than one. While these magnets are referred to as being cylindrical it is to be understood that this term is used in its broad geometrical sense and is not restricted to right circular cylinders. While right circular cylindrical magnets are a preferred embodiment it will be understood that other ellipsoidal and cylindrical shapes such as hexagons, octagons (cross-section), etc., may be used.

The location of these magnets is such that one magnet lies beneath each side 76 and 78 of the sector shaped coil 56, the magnets being placed so that opposite poles are uppermost in magnets 72 and 74 respectively. An upper shunt 80 is supported by a pair of sleeves 82 and 84 of soft magnetic material which extend through the pillar plate 44. Screws 86 and 88 pass through the upper shunt and sleeves 82 and 84. Both screws and sleeves engage the lower shunt 90 which is thus held against the bottom of the pillar plate. The pillar plate 44 is formed of a suitable nonmagnetic material such as brass or nickel silver, while the shunts 80 and 90 and sleeves 82 and 84 are formed of a magnetic material such as low carbon steel. The screws 86 and 88 may be either a magnetic or a nonmagnetic material, the sleeves 82 and 84 serving to connect the upper and lower shunt magnetically.

The lower shunt 90 is generally arcuate in shape and has a pair of radially inwardly extending projections 92 and 94 which extend under and into contact with the lower faces of the magnets 72 and 74. The upper shunt 80 is in the general form of a flattened M having outer legs 96 and 98 and an inner shallow V-shaped portion 100. Projecting from the lower surface of the shallow V- portion 100, as seen in Figure 1, are a pair of inverted V-disposed fingers 102 and 104.

Referring to Figure 4, it will be seen that neither legs 96 and 98 nor fingers 102 and 104 substantially overlie the upper surfaces of the magnets 72 and 74, the legs 96 and 98 extending to the outside of the magnets and the fingers 102 and 104 extending to the inside of the magnets. It will be noted that except for the ends of the upper shunt 80, which are fastened to sleeves 82 and 84, and except for the very tips of the fingers 102 and 104, the upper shunt does not substantially overlie the lower shunt 90. While the exact magnetic theory is not completely understood at this time, it has been found that this particular configuration coupled with the shape and size of the magnets results in a minimum of stray magnetic fields within the watch and provides a maximum uniform flux density through each of the sides 76 and 78 of the coil 56.

The longitudinal axes of the magnets are parallel to the balance staff and perpendicular to the plane of rotation of the balance wheel. After heat treatment and magnetization, magnets are permanently pressed into the pillar plate and are not handled by repairmen who might possibly assemble the magnets in an improper polarity relationship. The watch is anti-magnetic with respect to external magnetic fields and will continue to run and keep time in magnetic fields much larger than those which stop Watches commonly designated anti-magnetic. In the event of accidental magnetization of the balance staff or hairspring, the entire watch can be demagnetized by normal methods used by watchmakers without any effect on the Watch magnets or magnetic circuit.

Referring particularly to Figures 7 and 8, a modification of the shunt structure is shown in which slots are cut in the pillar plate 122 and U-shaped one piece shunts 124 are slid in position. The shunts overlie magnets 126 and are held in place by set screws 128. This modification produces a separate shunt circuit for each of the magnets and, while slightly different from the preceding structure, forrns an efifective magnetic circuit.

What is claimed and desired to be secured by United States Letters Patent is:

1. In a battery operated electric watch having an oscillating balance wheel carrying a periodically energized coil, a pair of cylindrical magnets creating a magnetic field in the path of movement of the coil, a first shunt connecting said magnets, said pair of cylindrical magnets having their magnetic axes disposed at right angles to each end of said first shunt, a second shunt bridging said poles above the plane of movement of the coil, said second shunt being formed with projecting fingers generally above said magnets to concentrate the magnetic field to approximately the effective width of the coil during its energization interval.

2. In an electric watch having a train and an electric source of motive power which includes a magnetic field, said field being produced by a pair of spaced magnets,

a first shunt member of soft magnetic material engaging one end of each magnet, and a second shunt member of soft magnetic material having portions thereof adjacent but spaced from the other ends of said magnets, said shunt members being so arranged that at least a portion of one shunt member does not overlie said second shunt member.

3. In an electric watch having a train and an electric source of motive power which includes a magnetic field, said field being produced by a pair of spaced magnets, a first shunt member of soft magnetic material having a body portion and having projections extending therefrom engaging one end of each magnet, and a second shunt member of soft magnetic material having a body portion and having fingers extending therefrom into proximity with but spaced from the other ends of said magnets.

4. In an electric watch having a train and an electric source of motive power which includes a magnetic field, said field being produced by a pair of spaced magnets, a first shunt member of soft magnetic material having a body portion and having projections extending there from engaging one end of each magnet, and a second shunt member of soft magnetic material having a body portion and having fingers extending therefrom into proximity with but spaced from the other ends of said magnets, said body portions being in non-overlying relationship.

5. A device as set out in claim 4 wherein the body portion of said first shunt member is generally arcuate and said projections extend towards the inside of said arc.

6. A device as set out in claim 5 wherein said fingers on said second shunt member are disposed in a V shape.

7. In an electric watch having a train and an electric source of motive power which includes a magnetic field, said field being produced by a pair of spaced magnets, a first shunt member having a body portion comprised of a central section and a pair of legs attached thereto, a pair of fingers extending from said central section, said legs and fingers extending into proximity with one end of each of said magnets and being so disposed that the longitudinal axes of said magnets do not intersect said legs or fingers, and a second shunt member engaging the other ends of said magnets.

8. In an electric watch having a train and an electric source of motive power which includes a magnetic field, said field being produced by a pair of spaced magnets, a first shunt member having a body portion comprised of a central section and a pair of legs attached thereto, a pair of fingers extending from said central section, said legs and fingers extending into proximity with one end of each of said magnets and being so disposed that the longitudinal axes of said magnets do not intersect said legs or fingers, and a second shunt member of generally arcuate shape having a pair of projections engaging the other ends of said magnets.

9. A device as set out in claim 8 wherein said central section of said first shunt member has a shallow V- shape.

10. In an electric watch having a train and an electric source of motive power which includes a magnetic field, said field being produced by a pair of spaced magnets having their magnetic axes parallel to one another, a first shunt member of soft magnetic material engaging one end of each magnet, and a second shunt member of soft magnetic material having portions thereof adjacent but spaced from the other ends of said magnets.

11. In an electric Watch having a train and an electric source of motive power which includes a magnetic field, said field being produced by a pair of spaced cylindrical magnets having their magnetic axes parallel to one another, a first shunt member of soft magnetic material engaging one. end of each magnet, and a second shunt member of soft magnetic material having portions there of adjacent but spaced from the other ends of said magnets.

12. In an electric watch having a train, a balance staff, a balance wheel and an electric source of motive power, a pair of spaced cylindrical magnets having their magnetic axes parallel to one another and parallel to said balance staff, shunt means engaging corresponding physical ends of said magnets and extending outwardly therefrom, and additional shunt means having portions associated with the other ends of said magnets and extending outwardly therefrom.

13. In an electric watch having a train, a balance staff, a balance wheel and an electric source of motive power, a pair of spaced cylindrical magnets having their magnetic axes parallel to one another and parallel to said balance staff, shunt means engaging corresponding physical ends of said magnets and extending outwardly there from, additional shunt means having portions associated with the other ends of said magnets and extending outwardly therefrom, and a member of soft magnetic material associated with each magnet and extending from the outwardly extending portion of said first named shunt means to the outwardly extending portion of said second shunt means.

14. In an electric watch having a pillar plate, a balance staff, a balance wheel, and an electric source of motive power, a pair of spaced cylindrical magnets fixedly mounted in said pillar plate and having their magnetic axes parallel to said balance staff, shunt means engaging said magnets on one side of said pillar plate, and additional shunt means on the other side of said pillar plate and associated with said magnets.

15. A device as set out in claim 14 including members of soft magnetic material extending between said first named shunt means and said additional shunt means.

16. A device as set out in claim 15 wherein said members extend through said pillar plate.

17. In an electric Wrist watch having a pillar plate, a gear train and a periodically energized oscillating coil passing through a magnetic field, magnetic circuit producing said magnetic field comprising a pair of permanent magnets having a length to diameter ratio of not greater than one, said magnets being press fitted into the pillar plate so that one end of each magnet extends above the pillar plate, a shunt connecting the magnet ends embedded in the pillar plate, supporting sleeves extending vertically from the ends of the shunts, a second shunt supported on the sleeves and extending partially over the free ends of the magnets, screws securing the second shunt, sleeves and first mentioned shunt to said pillar plate, the main portions of said second shunt being in a non-overlying relationship with said first mentioned shunt.

18. In an electric watch, a pair of permanent magnets, a shunt spaced from and opposing unlike poles of said magnets, said magnets and said shunt being so arranged that the fiux is in opposite direction, a balance wheel oscillating between said shunt and said magnets, a coil carried by said balance wheel, said coil having portions substantially radial to said wheel, the oscillatory move ment of said balance wheel carrying the radial portions of said coil through the magnetic fields between said magnet and said shunt, means for energizing said coil simultaneously with the passage of said radial portions through said magnetic fields.

19. In an electric wrist watch having a periodically energized frequency controlling element, a pair of permanent magnets creating magnetic fields in the path of movement of said frequency controlling element and having magnetic axes parallel to the axis of rotation of said frequency controlling element, a pair of shunts, one of said shunts connecting the ends of said magnets, the other of said shunts being located above said magnets and above the plane of rotation of said frequency controlling element and being so disposed that the greater part of the body of the upper shunt does not overlie the body of the lower shunt.

References Cited in the file of this patent 8 Holden Apr. 22, 1930 Conrad May 23, 1933 Fillinger Dec. 4, 1951 Held June 3, 1952 Ensign et a1. Apr. 28, 1959 

